It is generally known by those familiar with microbiology that the broad classifications of bacteria are heterotropic (air and water media) and autotropic (only water media). Generally speaking, heterotropic biology are aerobic, fast growing, and can fasten to bed materials, thereby holding their place in flowing water. On the other hand, autotropic biology are slow developing and go with the flow, unless captured or entangled by media, as very thin films on surfaces or in the still water muck.
Heterotrophs utilize readily available natural organic materials for growth and energy. Autotrophs gain energy and growth from the ammonia forms of nitrogen compounds, by oxidizing them to nitrite and nitrate, and use carbon dioxide as the oxidizing agent. Another type of autotroph uses nitrates to oxidize almost any type of organic material for growth and energy and produces nitrogen gas. Other autotrophs utilize sulfate and selenates as oxidizing agents and produce flowers of sulfur or red selenium metal. All types of heterotrophs and autotrophs are widespread in nature and in waste waters of domestic sources.
Normal and conventional practices in the art of water purification involve using separate units to favor heterotropic action and separate units designed to favor autotropic action.
It is generally known by those familiar with rice that the brown rice seed is contained within a hull which is approximately twenty percent silica. This hull is so much a part of the seed that it goes from farm to mill with the grain and, at the mill, it is removed by suitable roller action. Roller action at its best breaks the hull into two equal halves, dropping out the brown rice grain which is usually further polished to white rice. Each half of the hull looks like a tiny canoe, smooth on the inside and covered with uniform blisters on the outside, giving it the appearance of one half of an ear of corn on the outside. With twenty percent silica content, and little else other than cellulose and lignin, the hull has little food value and limited fuel value because of the high ash content. Furthermore, this ash is very fine and is a mucus irritant that will not clinker to aid disposal. When heated above about 1700.degree. F., this silica changes from the opaline form to quartz and crystalbalite.
The literature has many references to controlled burning and closed chamber pyrolysis of rice hulls. Both procedures, however, fail to describe the controlled conditions necessary to gain a high carbon content to the char. Both produce unwanted changes in the silica and both produce unwanted tars and oils in the off gases. In addition, the off gases contain nitrogen, carbon dioxide, nitrogen oxides, sulfur oxides, as well as the more desired hydrogen and carbon monoxide. Even following a most difficult gaseous separation, the hydrogen to carbon monoxide ratio is too low for most synthesis gas purposes. The off gas is therefore of low value as an energy fuel.
It is one object of the invention of my copending application, Ser. No. 06/576,209, incorporated herein by reference, to provide a process that assures that all silica from rice hulls remains in the opaline form, that as much carbon as possible remains in the valuable char, that tars and oils as by-products are eliminated, that nitrogen, carbon dioxide, nitrogen oxides and sulfur oxides do not appear in the off gases, and that the composition of the off gas is four atoms of hydrogen (2 molecules) to one molecule of carbon monoxide. The off gas produced according to such invention is almost exactly the synthesis gas that can be used to produce methyl alcohol by well-known means. While synthesis gas is normally made totally from natural gas, it is a purpose of that invention to gain most of the gas from an economical rice hull source. It is an additional purpose of that invention to make synthesis gas from other sources, namely other agricultural by-products, forest products and peat.
It is an object of this invention to use rice hulls for making a char most suited for an exceptional bio media, and a char most suited for making an exceptional activated carbon for color removal from liquid media. Generally, the practice of this portion of the invention is specific for the organic-color removal for waste water processes reverting the waste water to potable equivalent as specified in Federal Drinking Water Standards. The advantages and the economics realized in attaining clean water from waste water will become apparent from the following description.
It is a further object of this invention to provide a system in which the heterotropic and autotropic systems may be included in a single bed.
Yet another object of the invention is to provide a bed material for excellent biological filter media.
Still another object is to gain biological balances which minimize the bed time for treating waste waters.